1. Field of the Invention
The present invention relates to a measuring apparatus for measuring the concentration of a specific component of a liquid sample, particularly a turbid liquid sample.
2. Description of the Background Art
In a concentration measuring apparatus for a liquid sample, a pipeline comprising a valve having both of a channel connection switching function and a function of sealing an unnecessary piping channel is employed in case of separately guiding a plurality of reagents for measurement such as a moving phase of a buffer solution or the like, a standard solution and a washing solution from respective reservoirs to a reactor, a detector and the like. Such a valve is represented by a multi-way connecting valve.
Th e multi-way connecting valve can prevent contamination resulting from mixing of solutions at a terminal area, thereby attaining accurate measurement. When the sample is prepared from an extremely contaminative one such as a fermentation solution, for example, the detector is disadvantageously contaminated and reduced in accuracy.
When the sample solution is prepared from a fermentation solution or the like, the sample solution is kept seperate from a liquid flowing through a detecting mechanism until these solutions are brought into contact with each other through a film such as an ultrafiltration membrane, a dialysis membrane or a filter employed to prevent the detecting part from being contaminated with micro-organisms or the like. When the solutions are brought into contact with each other through the film, part of the sample solution or chemical substances dissolved therein is transferred into the liquid flowing in the detecting mechanism through the film.
The micro-organisms or a contamination source can be eliminated from the detecting part side by detecting the transferred sample solution or chemical substances.
Also when such a separation device having a film is employed, however, the sample solution generally contains a large quantity of gas such as carbon dioxide following proliferation of micro-organisms, in the case of a fermentation solution or the like. When such gas forms bubbles in the pipeline, the flow of the liquid is disturbed to readily cause reduction of accuracy.
In an apparatus having a separation mechanism through a film, further, pressure fluctuation may be transmitted to the film to cause reduction of accuracy when a plurality of sample solutions are switched.
When a sample is used, which contains a solid which tends to prevent a valve from sealing, not only sealing by the valve but switching of channels is made incomplete since the multi-way connecting valve performs switching of connection of the channels and sealing of unnecessary pipes by sliding of a valve element, and hence mutual contamination is disadvantageously readily caused by mixing of the solutions at the connecting part.
In order to open/close a pipe passing a solution containing a solid or the like therethrough, on the other hand, a valve, such as a pinch valve, for example, which presses and seals a pipe having elasticity over a length of several mm to several cm, for example, exceeding the inner diameter of the pipe is effective. Even if a solid of a size exceeding the inner diameter of the pipe enters the pipe, the valve presses and seals the pipe in a range beyond the size of the solid while the pressed elastic pipe is changed to the shape of the solid. Thus, the valve has high sealability for a sample containing a solid, although the same has no channel switching function. However, mixing of solutions at the pipe connecting part is unavoidable since the connecting part has no function of sealing unnecessary pipe channels. Thus, occurrence of mutual contamination and reduction of measuring accuracy are unavoidable.
When three pipelines for a standard solution, a sample solution and a washing solution, for example, are unified and guided to a pipeline reaching a measuring part with respect to such problems, there is a method of employing a four-way joint and connecting the three pipelines in one portion. In this method, the standard solution of a known concentration value and washing water are mixed into the sample solution in a certain ratio when the sample solution is passed, while it is conceivable that there is no problem if correction is performed. When the standard solution is passed, however, the sample solution of unknown concentration is mixed and hence no correct measurement result is obtained. Since the sample solution and the standard solution come into contact with each other, further, micro-organisms propagate in the connecting part through a nutrition source of a component of the standard solution such as glucose, for example, in case of a sample such as a fermentation solution containing micro-organisms, to unpreferably readily cause a problem such as clogging of the pipe by proliferated fungus bodies.
As a method of avoiding propagation of micro-organisms or the like, it is effective to construct a pipeline with employment of a three-way joint, so that the sample solution and the standard solution are not in direct contact with each other. Due to employment of the three-way joint, however, the state of contamination by mixing of the solutions is disadvantageously further complicated. When two or more pipelines are provided, pipe connecting parts are present in a plurality of portions due to employment of the three-way joint. Solution contamination is not necessarily caused at the same degrees in respective pipe connecting parts, leading to lack in reproducibility of measurement.
For example, there is a method of connecting reference and sample solution pipelines each comprising a pinch valve with each other by a three-way joint for joining the same with each other, and connecting the joined pipelines with a washing solution pipeline by another three-way joint, for guiding the same to a pump. In this piping state, however, the standard solution of constant concentration is regularly in contact with the sample solution having indeterminate concentration on an upstream connecting part, and no correct measurement result is obtained. This is because the concentration of the standard solution is instable since the concentration of a target substance in the sample solution is indeterminate, even if the degree of mutual contamination of the reference and sample solutions has reproducibility in view of only the rate of solution volumes. In these pipelines, further, the reference and sample solutions come into contact with each other, leading to a problem such as propagation of micro-organisms similarly to the case of employing a four-way joint.
There is another method of connecting sample and washing solution pipelines each comprising a pinch valve with each other by a three-way joint for joining the same, and connecting a standard solution pipeline comprising still another pinch valve to the joined pipelines by another three-way joint. In this case, the sample solution having indeterminate concentration or the washing solution which is contaminated with the sample solution having indeterminate concentration is regularly in contact with the standard solution. Further, positional difference is inevitably caused between the sample solution pipeline connecting part and the standard solution pipeline connecting part with respect to a pump, and difference is readily caused in degrees of transmission of suction force from the pump. Consequently, difference is readily caused between degrees of mutual contamination of the sample and washing solutions in a position separated from the pump and that in a position close to the pump. Thus, no reproducibility of measurement is attained but only an incorrect result of measurement is obtained in this case.
There is still another method of connecting reference and washing solution pipelines each comprising a pinch valve with each other by a three-way joint for joining the same, and connecting a sample solution pipeline comprising still another pinch valve to the joined pipelines by another three-way joint. In this case, the standard solution or the washing solution which is contaminated with the standard solution is regularly in contact with the sample solution while positional difference is inevitably caused between the sample solution pipeline connecting part and the standard solution pipeline connecting part with respect to a pump, and no reproducibility of measurement is attained but only an incorrect result of measurement is obtained also in this case.
Thus, it is difficult to form a channel while eliminating problems with respect to a sample containing solids, avoiding direct contact between sample and standard solutions, and attaining reproducibility of measurement.